How many silver coins, 1.75 cm in diameter and of thickness 2 mm, must be melted to form a cuboid of dimensions 5.5 cm × 10 cm × 3.5 cm?

Radius of silver coin (r) = 1.75/2 = 0.875 cm, height of silver coin (h₁) = 0.2 cm
Lenght of cuboid = 5.5 cm, breadth of cuboid = 10 cm Height of cuboid = 3.5 cm,
Let the number of coins = n
Therefore, n × volume of 1 silver coin = volume of cuboid
⇒ n(πr²h₁) = lbh ⇒ n × 22/7 × (0.875)² × 0.2 = 5.5 × 10 × 3.5
⇒ n = (5.5 × 10 × 3.5 × 7/0.875 × 0.875 × 0.2 × 22) ⇒ n = 400
Hence, the number of coins is 400.